Jacking apparatus for posttensioning concrete



P 3, 1968 w. F. KELLY 3,399,865

JACKING APPARATUS FOR POSTTENSIONING CONCRETE Filed June 27, 1966 2 Sheets-Sheet 1 INVENTOR Will/am EKeI/y ATTORNEYS Sept. 3, 1968 w. FL-KELLY 3,399,865

JACKING APPARATUS FOR POST-TENSIONING CONCRETE Filed June 27. 1966 2 Sheets-Sheet 2 fi7..'. 54 I Q i INVENTOR J William FKe/ly United States Patent 3,399,865 JACKING APPARATUS FOR POST- TENSIONING CONCRETE William F. Kelly, Avondale, La. (100 Bellaire Drive, New Orleans, La. 70124) Filed June 27, 1966, Ser. No. 560,463 Claims. (Cl. 25429) ABSTRACT OF THE DISCLOSURE lacking apparatus for post-tensioning concrete, including an elongated housing comprising an outer cylinder having a central bore, an inner cylinder spaced from said outer cylinder and having a longitudinal bore through which a tendon passes, the aft portion of the inner cylindrical member being reduced to provide an ejector member, a piston-like member positioned within the housing between said inner and outer cylinders, the piston-like member including a piston head, a shaft connected to the piston head, one end of the shaft being bored out to receive the inner cylinder, the outer terminal of the shaft being provided with a recess, a tendon-gripping assembly positioned in the recess, the tendon-gripping assembly including wedge segments for engagement with the tendon, a terminal of the wedge assembly being engaged by the ejection member upon completion of the jacking cycle, and power means for alternately applying pressure to both sides of the piston head to extend and retract the shaft.

This invention relates to jacking apparatus for postten'sioning concrete, and is particularly adapted for use in jacking a tendon through a concrete anchor of the type disclosed in my co-pending application, Ser. No. 490,421, filed Sept. 27, 1965.

It is an object of this invention to provide jacking apparatus of compact, portable construction, which is capable of efficiently and rapidly effecting jacking of a tendon through a live anchor until the desired tensioning stress has been placed thereon.

Another object is to provide tendon-jacking apparatus for post-tensioning concrete including a housing equipped with mechanism for gripping a tendon, the tendon extending coaxially through an anchor and the jacking apparatus, the tendon-gripping mechanism being carried by a ram movable lognitudinally of the housing, and power means for extending the ram to exert a tensioning stress on the tendon.

Other objects are to provide hydraulic jacking apparatus of the character described, with the addition of means for automatically releasing the gripping mechanism upon completion of a jacking cycle; to provide jacking apparatus which contacts only the live anchor, thereby obviating damage to the concrete, the engaging faces of the jacking apparatus and anchor being complementally formed to assure optimum operation at all times, and to provide jacking apparatus including spring means adapted to engage the jaw assembly of the live anchor, permitting limited movement thereof in a direction to permit tensioning of the tendon held by the anchor, and at the same time maintaining the ramming action to the jaw assembly.

Other objects of the invention will be manifest from the following description of the preferred form of the invention, taken in connection with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of the jacking apparatus of the present invention, illustrating the position of use before beginning the jacking operation;

FIG. 2 is a view similar to FIG. 1 illustrating the 3,399,865 Patented Sept. 3, 1968 initial position when initiating the jacking apparatus through a live anchor;

FIG. 3 is a view similar to FIG. 1 showing the jacking apparatus in fully engaged position with the live anchor;

FIG. 4 is a sectional view taken along the lines 4-4 of FIG. 2, looking in the direction of the arrows, and showing to advantage the manner of engagement of the jacking apparatus spring with the jaw assembly of the anchor;

FIG. 5 is a sectional view taken along the lines 5-5 of FIG. 2 looking in the direction of the arrows;

FIG. 6 is an enlarged, fragmentary, longitudinal sectional view showing to advantage the tendon-gripping mechanism being shown in operative position;

FIG. 7 is a view similar to FIG. 6, showing the wedge assembly in ejected or inoperative position;

FIG. 8 is a sectional View taken along the lines 88 of FIG. 6 looking in the direction of the arrows; and

FIG. 9 is a perspective view illustrating the application of the present invention.

Referring now in greater detail to the drawings, the jacking apparatus of the present invention is adapted to be used in conjunction with a live anchor 20 which is shown and described in my co-pending application, Ser. No. 490,421. Anchor 20 is adapted to be embedded in concrete 21, the anchor including a tapered casing 22, through which the tendon 23 to be tensioned, extends. A jaw assembly for gripping the tendon is indicated at 24, and a reaction plate on the outer periphery of the casing is indicated at 25. The outer terminal of casing 22 issues into an annular flange and primary reaction plate indicated at 26.

The device of the present invention preferably comprises a hydraulic jack of the central bore type, including a housing 27 having an axial bore extending therethrough, in which a piston-like member 28 is adapted to operate.

Housing 27 includes an outer cylinder 29, one end of which is closed by a wall member 30, which is fixed to cylinder 29 by welding or the like 31. Wall 30 includes a central bore 32, the inner portion of which is enlarged and threaded at 33 for engagement with a cylindrical member 34 through which tendon 23 passes. The aft portion of cylindrical member 34 is reduced as indicated at 35 to provide an ejector member adapted for cooperation with the tendon-gripping mechanism carried by piston-like member 28, in a manner to be hereinafter more fully described.

Wall 30 is additionally provided with a reduced extension 36 having a bore 37 which is aligned with bore 32 of wall 30, bore 37 issuing into an enlarged springreceiving bore 38 of substantially the same diameter as the outer diameter of a helical spring 39 adapted to be seated therein. Bore 38 in turn issues into a larger bore portion 40, which is adapted to permit limited expansion of spring 39 therein, upon compression. The outer face of extension 36 is provided with an annular recess as indicated at 41 to complement the contour of flange 26 of anchor casing 22, in order to insure proper engagement of the jacking apparatus with anchor 20. This is important in order to maintain the jacking apparatus coaxial with anchor 20 at all times during tensioning of tendon 23.

Cylinder 29 is provided with fittings 42 and 43 which are connected by hoses to a conventional source of hydraulic power for effecting operation of the present jack in a well known manner.

Piston-like member 28 includes a shaft 44, one end of which is bored out toreceive a cylindrical member 34. The inner terminal of member 28 is provided with a ram 45, which ram is adapted to abut wall 30 of cylinder 27 when the jacking apparatus is inoperative, the outer periphery of piston head 45 being proximate the inner periphery of cylinder 29. At a point intermediate its length, shaft 44 is provided with an internal abutment or stop 46 which extends inwardly to a point proximate ejector member 35. A wall member 47 is threadedly engaged at 48 with cylindrical member 27, wall 47 being provided with an enlarged central bore through which shaft 44 and its enclosed parts are adapted to pass. A plurality of sealing rings 49 are provided at strategic points.

The outer terminal of shaft 44 is provided with a recess adapted to receive a tendon-gripping assembly which is generally designated 50. The tendon-gripping assembly includes a cylindrical member 51 mounted in the terminal recess, which member is internally thickened to provide a gradually tapering interior wall, with the result that the internal diameter of the cylinder gradually decreases from one end thereof to the other, that portion which has the smallest diameter being remote from the terminal of the piston. In connection with tapering cylinder 51, there is provided a wedge assembly which includes a plurality of arcuate wedge segments 52, preferably three or more in number, which are shown to advantage in FIGS. 4 and 5, these wedge segments being provided with opposed tendon-gripping teeth 53 adapted to engage and hold tendon 23 during the jacking operation. It will be noted that wedge segments 52 abut ejector member 35 when the apparatus is in inoperative position. Tapered cylinder 51 is retained in place by a cap 54 threadedly engaged at 55 with the outer terminal of piston shaft 44, the cap being provided with a bore which permits insertion and ejection of wedge segments 52.

In use of the jacking apparatus of the present invention, tendon 23 is normally held in the pre-tensioned position by live anchor 20. Beyond anchor 20, exteriorly of concrete 21, the cable is trained through the central bore which extends axially through the jacking apparatus of the present invention, as shown in FIG. 1. At this time, wedge segments 22 are disengaged from tendon 23. Upon actuation of the jacking apparatus by feeding hydraulic fluid through fitting 42, housing 27 is moved relative to piston 28, resulting in engagement of the outer terminal of spring 39 with wedge assembly 24 of anchor 20 (see FIG. 2) thereby preventing accidental disengagement of the latter from the anchor casing. Ejection member 35 is also moved out of engagement with wedge assembly segments 52 of tendon-gripping assembly 50, thereby permitting relative movement of wedge segments 52 with respect to tapered cylinder 51.

In FIG. 3 there is illustrated the continued movement of cylinder 27 to compress spring 39. It will be noted that at this time, annual recess 41 of extension 36 is in contiguous engagement with the complemental portion of flange 26 and wedge segments 52 are in locked gripping engagement with tendon 23. Continued application of hydraulic pressure to piston 44 in a direction to cause movement thereof out of cylinder 29, results in movement of tendon 23 through anchor 20, thereby tensioning the latter. When pressure is exerted on tendon 23, the movement of the tendon tends to effect outward movement of jaw assembly 24 of anchor 20, thereby releasing the grip of the assembly on the tendon. Helical spring 39 permits limited movement of the wedge components of the assembly in order to release the gripping engagement of the latter with the tendon.

When piston 44 has moved to fully-retracted position, the engagement of ejector member 35 with wedge assembly segments 52 effects release of the gripping pressure of the jaws of the assembly on tendon 23 and the force of engagement of the ejector member causes the wedge assembly to be popped out of tapered cylinder 51 to the approximate position shown in FIG. 7. Release of the pull on the tendon causes a slight movement of the latter inwardly towards concrete 21 and simultaneous movement of jaw assembly 24 of anchor 20 into gripping engagement with tendon 23, thereby holding the tendon under tension.

Piston 44 is returned to its initial position by feeding fluid under pressure through fitting 43 to the opposite side of piston head 45, thereby returning the ram to its initial position proximate relationship to wall 30. Wedge segments 51 are then returned manually into tapered cylinder 51, thereby readying the jacking apparatus for the next jacking cycle. The cycle of operation is repeated as many times as necessary to effect the desired tension on cable 23.

With the apparatus of the present invention, coaxial relationship with the anchor is maintained at all times, even though the anchor may be canted in the concrete. There is additionally no likelihood of damaging the concrete surrounding the anchor and jacking apparatus since the latter does not contact the concrete at any time during the operation, the only contact being with the terminal of the live end anchor. With the present apparatus also, tension is constantly maintained on the tendon by virtue of the fact that when the tendon gripping assembly of the apparatus is operative, the corresponding part of the anchor is inoperative, and vice versa.

With the present apparatus also, a compact unit is provided which may be readily moved from one location to another very readily by one person and is quickly engaged with the tendon to be tensioned, the structure of the apparatus being such that no slippage of the tendon can occur.

While there has been herein shown and described a preferred form of the present invention, it is to be understood that such has been done for purposes of illustration only, and that various changes may be made therein, within the scope of the claims hereto appended.

I claim:

1. lacking apparatus for post-tensioning concrete including an elongated housing, front and rear walls closing both ends of said housing, said housing including spaced outer and inner cylinders, said inner cylinder being provided with a longitudinal bore through which a jacking tendon passes, one terminal of said inner cylinder providing an ejection member, said front wall being provided with a bore through which the tendon passes, a piston-like member, positioned between said inner and outer cylinders and movable relative thereto, said pistonlike member including a piston head, a shaft connected to said piston head, one end of said shaft being bored out to receive said inner cylinder, the outer terminal of said shaft extending through the rear wall of said housing and provided with a recess, a tendon-gripping assembly positioned in the recess, said tendon-gripping assembly including a cylindrical member, said cylindrical member being internally thickened to provide a gradually tapering interior wall, the thickest portion of the wall being remote from the outer terminal of said shaft, a wedge assembly including a plurality of Wedge segments removably positioned in said cylindrical member, said wedge segments having opposed teeth for engagement with a tendon passing therebetween, a terminal of said Wedge assembly being engaged by said ejection member of said inner cylinder upon completion of the jacking cycle, and power means for alternately applying pressure to both sides of said piston head to extend and retract said shaft.

2. The jacking apparatus of claim 1, with the addition of a reduced extension issuing from said front wall, a yieldable element seated in said reduced extension, said reduced extension and yieldable element having longitudinal bores through which the tendon passes.

3. The jacking apparatus of claim 2, wherein said yieldable element comprises a convolute spring.

4. The jacking apparatus of claim 3, wherein the outer terminal of said reduced extension is provided with an annular recess.

5. For use with a system for post-tensioning concrete which includes a live anchor having a casing terminating in an outer flange and a tendon-gripping jaw assembly movable within the casing, jacking apparatus for exerting stress on the tendon through the live anchor, the apparatus including a housing having an axial bore and comprising a cylinder, an end wall at one terminal of the cylinder, said end wall being provided with an extension having a central recess, the outer terminal of said cylinder end wall extension being provided with an annular recess for complemental engagement with the outer flange of the live anchor, yieldable means seated in the extension recess and extending beyond the longitudinal limit thereof, for engagement with the jaw assembly of the live anchor, the terminal of said extension being shaped for complemental engagement with the easing flange of the live anchor, a ram assembly operable longitudinally within said cylinder, hydraulic power means in communication with said cylinder for selectively effecting movement of said ram in either direction, a tendongripping assembly carried by said ram assembly adapted for engaging the tendon, said tendon-gripping assembly including wedge members having tendon-engaging teeth, to hold the tendon in fixed relation with respect to said ram assembly, during movement of the latter to place the tendon under tension, and an ejector member carried by said cylinder, said ejector member including a terminal portion engageable with said wed-ge members when the ram assembly is in fully retracted position.

References Cited UNITED STATES PATENTS 2,763,464 9/ 1956 Leonhardt 25429 3,090,598 5/1963 Paul v 254---29 3,099,109 7/1963 Hahn 52-223 3,176,961 4/1965 Glass 25429 3,207,829 9/1965 Nieber et al 254- 29 X 3,338,553 8/1967 Persicke 25429 FOREIGN PATENTS 1,124,587 7/ 1956 France.

20 MILTON S. MEHR, Primary Examiner. 

